The present invention relates to an apparatus and method for controlling the frequency of operation of the compressor in an air conditioning apparatus and more particularly, to the prevention of noise and vibrations caused by lower order harmonic frequency from generating in driving the compressor by inverter.
In a divided air conditioning apparatus which includes an outdoor device and indoor device, a control portion in the outdoor device includes a compressor. A microprocessor of the indoor device receives data regarding the compressor operation frequency through a key board and sends the operation frequency data produced by processing the indoor temperature and various requirements to the indoor device. The microprocessor of the outdoor device outputs control signals to the inverter drive portion so as to produce a PWM (Pulse Width Modulation) wave. The PWM wave is applied to the inverter, and the inverter generates a three phase AC power and applies the three phase AC power to the compressor, to power the compressor in the operation state as intended by the user.
When the compressor is driven by the inverter as described above, a lower order harmonic frequency is generated due to a magnetic distortion of the motor core and switch time deviations of power transistors comprising the inverter. Accordingly, the conventional compressor has a disadvantage in that it generates noise and vibrations as a result of the lower order harmonic frequency.
A typical example of preventing noise and vibrations from being generated in the compressor is disclosed in U.S. Pat. No. 4,186,334 wherein, a phase controller controls the DC output voltage of a rectifier. A power factor detector detects a phase controlling signal which outputs from a voltage/current controller for controlling the phase controller. The output signal of the power factor detector is added to a speed reference signal through an adder and subtracter. The speed reference signal is inputted to a frequency controller and the voltage/current controller to prevent the output current of the frequency controller and the torque of the motor from oscillating at a low frequency.
However, the invention does not solve the problem in that noise and vibrations are generated in the lower order harmonic frequency.